Patterned glass cylindrical lens arrays for concentrated photovoltaic systems, and/or methods of making the same

ABSTRACT

Certain example embodiments of this invention relate to patterned glass that can be used as a cylindrical lens array in a concentrated photovoltaic application, and/or methods of making the same. In certain example embodiments, the lens arrays may be used in combination with strip solar cells and/or single-axis tracking systems. That is, in certain example embodiments, lenses in the lens array may be arranged so as to concentrate incident light onto respective strip solar cells, and the entire assembly may be connected to a single-axis tracking system that is programmed to follow the East-West movement of the sun. A low-iron glass may be used in connection with certain example embodiments. Such techniques may advantageously help to reduce cost per watt related, in part, to the potentially reduced amount of semiconductor material to be used for such example embodiments.

This application is a division of application Ser. No. 12/662,628, filedApr. 26, 2010, the entire disclosure of which is hereby incorporatedherein by reference in this application.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to improved solarphotovoltaic systems, and/or methods of making the same. Moreparticularly, certain example embodiments of this invention relate topatterned glass that can be used as a cylindrical lens array in aconcentrated photovoltaic application, and/or methods of making thesame. In certain example embodiments, the lens arrays may be used incombination with strip solar cells and/or single-axis tracking systems.Such techniques may advantageously help to reduce cost per watt related,in part, to the potentially reduced amount of semiconductor material tobe used for such example embodiments.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Photovoltaic devices are known in the art (e.g., see U.S. Pat. Nos.6,784,361, 6,288,325, 6,613,603, and 6,123,824, the disclosures of whichare hereby incorporated herein by reference). Some conventionalmainstream photovoltaic modules use a large number of crystallinesilicon (c-Si) wafers. The inclusion of the large number of c-Si waferstends to dominate the cost of the overall photovoltaic module. Indeed,about 60% of the costs involved in the production of conventionalphotovoltaic modules is related to the c-Si solar cells. To address thisissue, concentrated photovoltaic (CPV) systems have been proposed, inwhich the sunlight is to be focused with concentration ratios of 100× to1000×. Calculations suggest that a concentration ratio of approximately10× should enable a photovoltaic system to be produced that uses atleast 90% less silicon material.

Unfortunately, however, current concentrated photovoltaic systems useexpensive high efficiency multi-junction solar cells, expensivedual-axis tracking systems, and/or relatively expensive concentratingoptics. Therefore, these systems have difficulty competing with otherphotovoltaic solutions on a cost per watt basis.

Thus, it will be appreciated there is a need in the art for a simplelow-cost CPV systems, together with low cost solar cells and low-costconcentrating optics, and/or methods of making the same.

One aspect of certain example embodiments relates to a patterned glasscylindrical lens array, and/or methods of making the same.

Another aspect of certain example embodiments relates to using such acylindrical lens array to focus light on substantially elongate or stripsolar cells.

Another aspect of certain example embodiments relates to one-axistracking systems, and/or methods of making and/or using the same.

In certain example embodiments of this invention, a method of making alens array for use in a solar photovoltaic module is provided. Glass ismade using a float process including a float glass line. The glass ispatterned using a plurality of rollers disposed along the float glassline so as to form a plurality of first lenses oriented along a commonaxis. The rollers each have profiles such that each said first lens ispatterned to have at least one convex major surface when viewed in sidecross section.

In certain example embodiments of this invention, a method of making asolar photovoltaic module is provided. A lens array comprising aplurality of lenses oriented along a common axis is provided, with thelenses being patterned using rollers disposed along a float glass line,and with the lenses each having at least one convex major surface whenviewed in side cross section. A plurality of elongate solar cells isprovided, with each said solar cell comprising c-Si. The lens array isoriented relative to the solar cells such that each said lens isarranged to concentrate light incident thereon in substantially onedimension on the elongate solar cells. In certain example instances, asolar photovoltaic module is made in this way, and the photovoltaicmodule is connected to a single-axis tracking system at a fixed tilt,with the single-axis tracking system being movable so as to match theEast-West movement of the sun.

In certain example embodiments of this invention, a method of making asolar photovoltaic system is provided. At least one lens arraycomprising a plurality of lenses oriented along a common axis isprovided, with the lenses being patterned using rollers disposed along afloat glass line, and with the lenses each having at least one convexmajor surface when viewed in side cross section. The at least one lensarray is oriented relative to a plurality of elongate solar cellscomprising c-Si such that each said lens is arranged to concentratelight incident thereon in substantially one dimension on the elongatesolar cells. The at least one lens array and the plurality of elongatesolar cells are built into a single-axis tracking system that is movableso as to match the East-West movement of the sun.

In certain example embodiments of this invention, a method of making asolar photovoltaic system is provided. At least one lens arraycomprising a plurality of lenses oriented along a common axis isprovided, with the lenses being patterned using rollers disposed along afloat glass line, and with the lenses each having at least one convexmajor surface when viewed in side cross section. Tubing is provided on anon-light incident side of the at least one lens array, with the tubingbeing suitable to convey liquid therethrough and having at least oneelongate solar cell comprising c-Si disposed thereon proximate to orover a liquid input location. The at least one lens array is orientedrelative to the tubing each said lens is arranged to concentrate lightincident thereon in substantially one dimension on the tubing such that,in operation, electricity is generated via the at least one elongatesolar cell and such that the liquid is heated from an initialtemperature at the liquid input location to an elevated temperature asthe liquid moves through the tubing to a liquid output location.

In certain example embodiments of this invention, a photovoltaic systemis provided. A plurality of elongate solar cells is provided, with eachsaid solar cell comprising c-Si. A lens array comprising a plurality oflenses oriented along a common axis is provided, with each said lensbeing configured to concentrate incident light in substantially onedimension the elongate solar cells, and with each said lens having aconcentration ratio of 3×-30×.

In certain example embodiments of this invention, a photovoltaic systemis provided. A plurality of elongate solar cells is provided. A lensarray comprising a plurality of lenses oriented along a common axis isprovided, with each said lens being configured to concentrate incidentlight in substantially one dimension on the elongate solar cells. Asingle-axis tracking system is provided, with the single-axis trackingsystem being configured to move the lens array and/or the plurality ofelongate solar cells so as to substantially match the East-West movementof the sun. Each said lens has a convex top and/or bottom surface whenviewed in side cross section. The lens array is patterned from a singlelow-iron glass substrate.

In certain example embodiments of this invention, a photovoltaic systemis provided. At least one lens array comprising a plurality of lensesoriented along a common axis is provided, with the lenses beingpatterned from low iron float glass along a float glass line, and withthe lenses each having at least one convex major surface when viewed inside cross section. Tubing is provided on a non-light incident side ofthe at least one lens array, with the tubing being suitable to conveyliquid therethrough and having at least one elongate solar cellcomprising c-Si disposed thereon proximate to or over a liquid inputlocation. The at least one lens array is oriented relative to the tubingsuch that each said lens is arranged to concentrate light incidentthereon in substantially one dimension on the tubing to generateelectricity via the at least one elongate solar cell and to heat theliquid from an initial temperature at the liquid input location to anelevated temperature as the liquid moves through the tubing to a liquidoutput location.

In certain example embodiments of this invention, a building product isprovided. A plurality of elongate solar cells comprising c-Si issupported by a cover glass substrate. A lens array comprises a pluralityof lenses oriented along a common axis, with each said lens beingconfigured to concentrate incident light in substantially one dimensionon the elongate solar cells, and with the lens array being substantiallyparallel to and spaced apart from the cover glass substrate. Each saidlens has a convex top and/or bottom surface when viewed in side crosssection. The lens array is patterned from a single low-iron glasssubstrate. In certain example instances, a frame may be structured tomaintain the lens array and the cover glass substrate in parallel spacedapart relation.

In certain example embodiments of this invention, a method of making asolar photovoltaic module is provided. An array comprising a pluralityof reflective elements oriented along a common axis is provided, withthe array being patterned using rollers disposed along a float glassline, and with the reflective elements each having a concave majorsurface when viewed in side cross section. A plurality of elongate solarcells is provided on a glass substrate, with each said solar cellcomprising c-Si. The array is oriented relative to the substrate suchthat each said reflective element is arranged to concentrate lightincident thereon in substantially one dimension on the elongate solarcells.

In certain example embodiments of this invention, a solar photovoltaicmodule is provided. An array comprises a plurality of reflectiveelements oriented along a common axis, with the array being patternedfrom low iron float glass, and with the reflective elements each havingat least one concave major surface when viewed in side cross section. Aplurality of elongate solar cells is provided on a glass substrate, witheach said solar cell comprising c-Si. The array is oriented relative tothe substrate such that each said reflective element is arranged toconcentrate light incident thereon in substantially one dimension on theelongate solar cells.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is an illustrative linear focusing concentrating photovoltaicsystem including a cylindrical lens array made from patterned glassaccording to an example embodiment;

FIG. 2 is a schematic view of illustrative top and bottom rollerprofiles that may be used in a patterning line to obtain the lens arrayof certain example embodiments;

FIG. 3 shows example dimensions of lenses in a lens array in accordancewith an example embodiment;

FIG. 4 is a graph showing the approximate cost per watt vs.concentration ratio (CR) of various different concentrating photovoltaicsystems;

FIG. 5 is a schematic view of an illustrative one-axis tracking systemincorporating concentrating lens arrays in accordance with an exampleembodiment;

FIG. 6 is a schematic view of two plano-convex arrays being laminatedtogether in accordance with an example embodiment;

FIG. 7 is a schematic view of a Fresnel-type lens array in accordancewith an example embodiment;

FIG. 8 is a hybrid thermal solar panel system that incorporates a lensarray and strip solar cells in accordance with an example embodiment;

FIG. 9 is an illustrative system that incorporates a patterned mirrorarray and strip solar cells in accordance with an example embodiment;and

FIG. 10 is a flowchart showing an example method of making aphotovoltaic system in accordance with an example embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Photovoltaic devices such as solar cells convert solar radiation intousable electrical energy. The energy conversion occurs typically as theresult of the photovoltaic effect. Solar radiation (e.g., sunlight)impinging on a photovoltaic device and absorbed by an active region ofsemiconductor material generates electron-hole pairs in the activeregion.

Certain example embodiments of this invention relate to patterned glassthat can be used as a cylindrical lens array in a concentratedphotovoltaic application, and/or methods of making the same. In certainexample embodiments, the lens arrays may be used in combination withstrip solar cells and/or single-axis tracking systems. That is, incertain example embodiments, lenses in the lens array may be arranged soas to concentrate incident light onto respective strip solar cells, andthe entire assembly may be connected to a single-axis tracking systemthat is programmed to follow the East-West movement of the sun. Alow-iron glass may be used in connection with certain exampleembodiments. Such techniques may advantageously help to reduce cost perwatt related, in part, to the potentially reduced amount ofsemiconductor material to be used for such example embodiments.

As indicated above, certain example embodiments relate to patternedglass cylindrical lens arrays, and/or methods of making the same. Inthis regard, FIG. 1 is an illustrative linear focusing concentratingphotovoltaic system including a substantially cylindrical lens arraymade from patterned glass according to an example embodiment. A largeflat low iron glass plate is modified into a lens array 1 byperiodically modifying its thickness, e.g., at regular intervals. Thelenses 3 a-3 d in the lens array 1 focus the sunlight from the sun insubstantially one dimension, with a concentration ratio of, for example,3× to 30×. The solar radiation may be focused on, for example, c-Sisolar cells, with an efficiency of up to 20%. Such c-Si solar cells arecommercially available at reasonable costs. FIG. 1 shows the c-Si solarcells being formed as strips 5 a-5 d. Further details regarding thesestrip solar cells 5 a-5 d are provided below. In any event, the c-Sisolar cells may be provided on one or more opaque or transparentsubstrates in different embodiments of this invention. The lenses 3 a-3d in the lens array 1 are provided substantially in-line along a commonaxis. The lenses 3 a-3 d may be formed from a single piece of glass incertain example embodiments. In such cases, the lenses 3 a-3 d mayeffectively be connected to one another by virtue of being formed from acommon glass substrate. Alternatively or in addition, multiple lensesand/or lens arrays may be provided adjacent to one another in differentexample embodiments of this invention.

A patterning line in a float glass factory may be used to create thelarge area cylindrical lens array of certain example embodiments. Thiscan be done by using one or more sets of top and bottom rollers with theexample profile shown in FIG. 2. That is, FIG. 2 is a schematic view ofillustrative top and bottom roller profiles that may be used in apatterning line to obtain the lens array of certain example embodiments.When viewed in cross-section, the individual top and bottom rollers 7a-7 d and 9 a-9 d in the top and bottom roller arrays 7 and 9 areconcave at the top and bottom. Thus, the rollers of FIG. 2 will lead toa convex-convex lens array. Of course, it will be appreciated that aplano-convex lens array may be obtained, as well, when either the top ofbottom set of rollers is flat.

FIG. 3 shows example dimensions of lenses in a lens array in accordancewith an example embodiment. Each lens in the FIG. 3 example has a pitchor width that ranges from approximately 10-100 mm, a minimum thicknessor height from about 2-4 mm, and a maximum thickness or height of about4-8 mm. Depending on the pitch, the focal length will be about 10-200mm, e.g., from or proximate to the center of the individual lenses. Ofcourse, it will be appreciated that the dimensions specified in FIG. 3are provided by way of example. Indeed, different embodiments of thisinvention may include differently sized, shaped, and/or focal lengthlenses. For instance, the minimum thickness or height of certain exampleembodiments may be about 2 mm and the maximum thickness or height ofcertain example embodiments may be about 8 mm. In certain exampleembodiments, a 1 m² module may comprise about 10-50 lenses. The FIG. 3example has a width of 25 mm, a minimum thickness of 3 mm, and a maximumthickness of 4 mm. These dimensions imply a height difference of 1 mmand 40 lenses per 1 m² module. In example instances, the focal lengthwill be 150 mm, and the lens-solar cell distance may be placed at 135 mmto achieve a concentration ratio of about 10. Placing the solar cellcloser to the focal point may be advantageous in certain exampleinstances so that light is concentrated on a larger area of the solarcell.

Any suitable transparent substrate may be used in connection withcertain example embodiments of this invention. For instance, certainexample embodiments may incorporate a low-iron glass substrate, e.g., tohelp ensure that as much red and near-IR light as possible istransferred to the semiconductor absorber layer. Example low-iron glasssubstrates are disclosed, for example, in co-pending and commonlyassigned application Ser. Nos. 11/049,292; 11/122,218; 11/373,490;12/073,562; 12/292,346; 12/385,318; and 12/453,275, the entire contentsof each of which are hereby incorporated herein by reference.

For instance, certain example embodiments may incorporate a hightransmission low iron glass, which is highly oxidized and made using thefloat process. In certain example embodiments, the glass compositionused for the glass is made via the float process using an extremely highand positive batch redox in order to reduce % FeO to a low level andpermit the glass to consistently realize a combination of high visibletransmission (Lta or Tvis), high infrared (IR) transmission, and hightotal solar (TS) transmission. Further details of example low iron glassare provided below.

In addition, the low iron glass may be thermally tempered. Suchtempering may occur in certain example embodiments at the end of theproduction line, e.g., after the glass has been patterned in certainexample instances.

Current CPV systems typically implement two-axis tracking because theyuse two-dimensional focusing. In this regard, current CPV systemsusually are mounted on poles with individual tracking for each unitsystem. This arrangement increases the cost of the system. By contrast,certain example embodiments that implement cylindrical lens arraysreduce (and sometimes completely eliminate) the need for dual-axistracking. This is because the cylindrical lens arrays of certain exampleembodiments are configured to linearly focus sunlight on or along astrip as opposed to a smaller point or spot location. Indeed, when thecylindrical lenses of certain example embodiments are orientedsubstantially vertically, simple East-West one-axis tracking may beimplemented easily and efficiently.

In Table 1 the annual energy outputs from a 20% efficient system at anexample location (Phoenix, Ariz.) are compared for fixed latitude tilt,one-axis tracking, and two-axis tracking systems. More particularly, thesolar cells are high efficiency, back contact solar cell stripscommercially available from Sunpower. The improvement in energy outputgoing from a fixed orientation system to a one-axis tracking system is30.7%. This is a very significant gain. However, the improvement ofmoving from a one-axis tracking system to a dual-axis tracking system isonly an additional 5.8%. This additional 5.8% energy gain typically isoffset by the expense of the dual-axis tracking system itself. Currentdual-axis tracking systems therefore are not seen as economical. In anyevent, certain example embodiments that implement a linearly focusedsystem are able to realize at least the efficiency gains associated withmoving from a single-axis tracking system to dual-axis tracking systemwithout actually having to incur the expenses associated with thedual-axis tracking system because such embodiments may be implementedwith only one-axis tracking systems.

TABLE 1 Annual energy output per m² incident sunlight for fixedorientation, one-axis tracking, and two-axis tracking systems in Phoenix(based on NREL PVWatts Calculator) Annual energy generation (kWh/m²/yr)Fixed orientation One-axis Two- PV Conversion (On roof) E-W axistechnology Efficiency Lat. tilt tracking tracking Phoenix High eff. 20%386.53 505.52 534.80 c-Si 33° 43° N ~100% ~131% ~138%

It will be appreciated that certain example embodiments are advantageousfor a number of reasons. For instance, single-axis tracking can beimplemented at low cost, because many modules can be oriented with asingle actuator by connecting all modules to each other through parallelbeams. The lens array is oriented substantially vertically and istherefore largely self-cleaning, as rain will flow down in the groovesof the patterned glass and reduce the amount of dust accumulation.Additional periodic cleaning optionally may be implemented, of course.Single-axis tracking systems also may be low to the ground, as themechanisms for moving it are simplified compared to the mechanisms usedfor two-axis tracking systems.

The solar cells in the FIG. 1 example system may be manufacturedeconomically, e.g., by cleaving strips from c-Si solar cells. Forinstance, a larger (e.g., 4 inch to 12 inch) wafer may be formed andsubsequently cleaved to produce a plurality of strips. For concentrationratios of 3× to 30×, only about 33% to 3.3% silicon is needed, ascompared to conventional c-Si modules without concentration which mayrequire higher amounts of silicon.

As alluded to above and as suggested in the use of the term “strip”itself, the strip solar cells of certain example embodiments may have asubstantially elongated shape. For instance, certain example strip solarcells may be 2 mm×150 mm, although other dimensions also are possible.In any event, the strip solar cells may be cleaved along the directionof its crystal orientation. The strip cells optionally may be mounted ona second glass substrate or another type of substrate in certain exampleembodiments. In so doing, the second substrate may be made to functionas a heat sink, thereby helping to keep the operating temperature of thesolar cells low and their efficiency high. Active cooling may be used inplace of, or in addition to, such heat sink techniques in certainexample embodiments.

In connection with example embodiments that implement strip solar cells,low-cost assembly techniques known and commonly used in, for example,the flat panel display (FPD) industry, may be used. For example, suchtechniques may readily be used in connection with strip solar cellshaving a width of 2-20 mm, and such techniques may include, for example,chip on glass (COG) manufacturing. These COG manufacturing techniquesmay, in turn, incorporate interconnecting wires such as, for example,patterned metals provided on the glass, copper tape, and/or the like.Certain example embodiments may incorporate solar cells with low shadingor non-shading interconnects. Non-shading interconnects sometimes areused, for example, in back contact solar cells (e.g., available fromSunpower).

FIG. 4 is a graph showing the approximate cost per watt vs.concentration ratio (CR) of various different concentrating photovoltaicsystems. The FIG. 4 graph is based on the following assumptions. For CRsgreater than 100, expensive multi-junction GaAs cells need to be usedwith active cooling. For CRs greater than 100, two-dimensionalconcentration is needed with dual-axis tracking. For CR less than 100,one-dimensional (e.g., cylindrical) concentration is used along withsingle-axis tracking. The cost per watt for the solar cell includescosts associated with packaging and interconnects, and the cost per wattfor the concentrating optics includes costs associated with alignment.The FIG. 4 graph allows efficiency to exceed 20%. As will be appreciatedfrom the FIG. 4 graph, a concentration ratio of about 10-30× isparticularly desirable from a cost per watt perspective.

It will be appreciated that there are a number of advantages associatedwith certain example embodiments of this invention. For example, the 3×to 30× concentration optics may be produced easily and inexpensivelyusing patterned glass. This may, in turn, also allow for a 3× to 30×smaller area of c-Si solar cells. Cylindrical lens arrays may besubstantially self-cleaning when installed vertically at a latitude tiltin certain example implementations, as the amount of dust and/or otherdebris that will accumulate will be reduced, since rain will clean thegrooves of the vertically positioned patterned glass lens array. Certainexample embodiments also enable low cost and known, reliable assemblytechniques from the FPD industry to be used in connection with stripsolar cells (e.g., when they are provided with a width of about 2-20mm). Also, as explained in detail above, the use of low-cost single-axistracking systems may in certain example embodiments advantageouslyimprove power output by about 30% as compared to fixed orientationsystems. Furthermore, many modules may be easily connected to the samesingle-axis tracking system. The use of such example techniques in highdirect-insolation areas such as the Southwest USA may lead to higherannual energy output.

FIG. 5 is a schematic view of an illustrative one-axis tracking systemincorporating concentrating lens arrays in accordance with an exampleembodiment. The illustrative system in FIG. 5 includes a plurality ofconcentrating lens array modules 11. Each such module 11 may be the sameas or similar to the arrangement shown in FIG. 1, for example. That is,each module may include a lens array that concentrates light on stripsolar cells, e.g., of c-Si. The individual modules 11 may be connectedto a common power source, e.g., using interconnects 12. The modules 11also may be controlled such that they move in a direction that matchesthe East-West movement of the sun.

In certain example embodiments, antireflective (AR) coatings may beprovided to one or both sides of the lens array to increasetransmission. In certain example embodiments, a broadband AR may beprovided using any suitable technique. In certain example instances, alow index silicon oxide (e.g., SiO₂ or other suitable stoichiometry)coating having an index of refraction of about 1.3 may be provided onone or both sides of a lens array through a wet application process(e.g., a dip, spray, roll, or other coating process), for a sol, forexample. Such a technique may lead to for example, a 3-6% increase inlens array transmission and/or module power, depending on the coatingused and the number of surfaces coated.

In certain example embodiments, the lens array may be heat strengthenedand/or thermally tempered. Of course, thermal tempering may be difficultto accomplish in connection with patterned glass having varyingthicknesses. Chemical tempering and/or strengthening techniquestherefore may be used in connection with certain example embodiments.

As another alternative or addition, lens arrays may be laminatedtogether, e.g., as shown in FIG. 6, which is a schematic view of twoplano-convex arrays being laminated together in accordance with anexample embodiment. In FIG. 6, first and second plano-convex arrays 13 aand 13 b are provided. The first and second plano-convex arrays 13 a and13 b are laminated together using any suitable laminate material 15. Forinstance. PVB, EVA, or the like may be used to laminate together thefirst and second plano-convex arrays 13 a and 13 b. The individualarrays 13 may be individually strengthened or tempered (thermally,chemically, or otherwise) in certain example instances, as thevariations in thickness may be less severe and thus easier to process incomparison to convex-convex type lens arrays. In certain exampleinstances, the laminate 15 itself may help to strengthen the overallarray.

FIG. 7 is a schematic view of a Fresnel-type lens array in accordancewith an example embodiment. As is known, Fresnel lenses generally havelarge apertures and short focal lengths, without the weight and volumeof material that would be required in conventional lens design. Inaddition, Fresnel lenses tend to be thinner, thereby allowing more lightto pass through them. The comparatively lower thickness variation mayenable Fresnel lenses to be tempered. Although the example lens in FIG.7 is patterned on both major axes, it will be appreciated that one sideof the lens may be planar or substantially planar and the other side maybe patterned. In certain example embodiments, such lenses having oneplanar side and one Fresnel patterned side may be laminated together,e.g., using the techniques and/or materials described above.

FIG. 8 is a hybrid thermal solar panel system that incorporates a lensarray and strip solar cells in accordance with an example embodiment.The FIG. 8 example system is similar to the FIG. 1 example system inthat it includes a lens array having a plurality of lenses 3 a-3 d, anda plurality of strip solar cells 5 a-5 b. Light from the sun is focusedon the strip solar cells 5 a-5 b to produce electricity. The FIG. 5example hybrid system also includes tubing 17 a and 17 b through whichwater or another suitable fluid may flow. Cool water is fed into thetubing 17 a and 17 b proximate to the strip solar cells 5 a-5 b,continues in a path (which in the FIG. 8 example embodiment issubstantially U-shaped), and exits remote from the strip solar cell.Providing cool water proximate to the strip solar cells is advantageousin that it improves the efficiency of the c-Si. In this regard, it isknown that the efficiency of c-Si solar cells drops significantly athigher temperatures (e.g., at 60 degrees C.) and improves at lowertemperatures (e.g., at 25 degrees C.). The provision of cooler waterproximate to the strip solar cells therefore may improve the operationalefficiency of the system.

Although the presence of cooling water may increase efficiency of anindividual strip solar cell, the overall solar cell efficiency may bedecreased by providing fewer total solar cells, e.g., because a solarcell may not be provided along the return path for the hot output water.Nevertheless, overall efficiency may be improved by virtue of thecooling water's effect on the strip solar cells that are present and thefurther heating of the water via the lens array throughout the entirepath, including the return path (where there is no solar cell). Theheated water, of course, may be used as it otherwise would be used inconnection with a thermal solar power application. As explained ingreater detail below, the lens array and/or the tubing may move relativeto one another, e.g., so as to match the East-West movement of the sun.This may be advantageous, for example, in building-integratedphotovoltaic (BIPV) applications.

Focusing additionally or alternatively may be performed using apatterned mirror array. FIG. 9 is an illustrative system thatincorporates a patterned mirror array and strip solar cells inaccordance with an example embodiment. In FIG. 9, strip solar cells 3a-3 d are provided, directly or indirectly, on a cover glass substrate19. For instance, the cover glass substrate 19 may be closer to the sun,and the strip solar cells 3 a-3 d in certain example instances may beprovided on a major surface of the cover glass substrate 19 opposite thesun. In certain example embodiments, the cover glass substrate may bemade from low iron float, glass. In certain example embodiments, an ARcoating may be applied thereto. Light passing through the cover glasssubstrate 19 may be reflected and concentrated back towards the stripsolar cells 3 a-3 d using a mirror array 21. The mirror array 21 may bea piece (or multiple pieces) of patterned glass that has been coatedwith a reflective coating. Light impinging on the troughs or concaveareas 21 a-21 d in the mirror array 21 therefore may be reflected backtowards the strip solar cells 3 a-3 d. As above, relative movement ofone or both of the cover glass substrate 19 and the mirror array 21 maybe caused so as to improve efficiency (e.g., by tracking the East-Westmovement of the sun).

Although certain example embodiments have been described in connectionwith a fixed or stationary solar cell module and a moving lens array,certain other example embodiments may involve a fixed or stationary lensarray and a moving solar cell module. In the latter case, the lens arraymay be stationary at a fixed orientation, and the solar cell array maybe configured to move during the day to maintain the focus of the lightfrom the sun on the strip solar cells, e.g., to match the East-Westmovement of the sun. In this regard, the strip solar cells may beprovided on a substrate as described above, and the substrate may bemade to move. Such example embodiments may be used, for instance, inconnection with building-integrated photovoltaic applications, similarto self-regulating windows. Self-regulating windows are known todynamically adjust the amount of light passing therethrough, e.g., usingdiffusers, blinds, or the like. In certain example embodiments, themovement of the sun may be tracked (directly or indirectly, e.g., basedon time of day and/or day of year) so that the substrate may be movedappropriately to increase or maximize the amount of sunlight impingingon the solar cells. It will be appreciated that diffuse light may betransmitted in such instances, and direct sunlight may be converted intoelectricity by the photovoltaic cells.

Certain example embodiments may be used as windows, skylights,roof-mounted PV modules, or the like in connection with BIPVapplications. For example, in rooftop applications, full size solarcells may be replaced with strip cells. Thinner (e.g., 1-2 mm thick),flat or non-patterned glass may be used as cover glass in BIPVapplications. To protect the strip solar cells, a UV and/orweather-resistant backsheet may be provided. For instance, Tedlar, whichis commercially available from Dupont, is a PVF film that may be used asa backsheet. Of course, it will be appreciated that other materials maybe used, provided that they perform functions such as, for example,vapor barrier protection, physical protection of wiring and/or othersensitive components, electrical insulation, heat reduction, etc. Thestrip solar cells thus may be sandwiched between a cover glass sheet anda protective backsheet. The backsheet may be transparent or opaque,depending on the desired application. In any event, the lens array maybe provided in substantially parallel spaced apart relation to the stripsolar cell sandwich. Known tabbing, framing, and junction box technologymay be leveraged to help provide BIPV applications.

It will be appreciated from the description above that certain exampleapplications may be structured somewhat similarly to insulating glass(IG) units. The first or outer pane may be the cylindrical lens array,whereas the second or inner pane may have the strip solar cells formedthereon. Rather than spacers, window frame components may help maintainthe panes in substantially parallel, spaced apart relation to oneanother, e.g., at the appropriate focal length. In certain exampleembodiments, when the lens array has a flat surface, this side may faceoutwardly, e.g., towards the sun. Of course, providing patterned glassmay be viewed as a desirable aesthetic feature in certain exampleinstances, and a patterned surface may face outwardly in such cases.

The following table compares cost per watt for various types ofphotovoltaic technologies.

TABLE 2 Estimated Cost per Watt for Photovoltaic Technologies UsingPhoenix, Arizona as an Exemplary Location Annual Power Cost Output perm² per Efficiency Tracking Module Area Watt Polycrystalline silicon 15%None 290 kWh $1.40 Thin film CdTe 11% None 212 kWh $0.98 (e.g., FirstSolar) Example 20% One-Axis 505 kWh $0.85 (e.g., Lens Array) East-West

As can be seen, the example in Table 2 produces 2.4× higher output persquare meter as compared to CdTe type photovoltaic systems for directsunlight. The example in Table 2 also provides a potentially lowercost/watt compared to CdTe type photovoltaic systems.

FIG. 10 is a flowchart showing an example method of making aphotovoltaic system in accordance with an example embodiment. Floatglass (e.g., low iron float glass) is patterned using a plurality of topand bottom rollers to form a lens array comprising a plurality of lensesoriented along a common axis in step S101. In step S103, a c-Si thinfilm is formed on a wafer and, the wafer is cleaved along the c-Sicrystal orientation into a plurality of elongate solar cells in stepS105. The elongate solar cell strips are provided in substantiallyparallel spaced apart relation to one another in step S107. In stepS109, the lens array is oriented relative to the solar cells such thateach said lens is arranged to concentrate light incident thereon insubstantially one dimension on one respective elongate solar cell.Optionally, in a step not shown, the lens array and the plurality ofelongate solar cells may be mounted to a single-axis tracking system,with the single-axis tracking system being-programmed to move so as tosubstantially match the East-West movement of the sun, e.g., to maximizethe amount of light incident on the lens array and concentrated on thestrip solar cells.

As indicated above, certain example embodiments may include low-ironglass. The total amount of iron present is expressed herein in terms ofFe₂O₃ in accordance with standard practice. However, typically, not alliron is in the form of Fe₂O₃. Instead, iron is usually present in boththe ferrous state (Fe²⁺; expressed herein as FeO, even though allferrous state iron in the glass may not be in the form of FeO) and theferric state (Fe³⁺). Iron in the ferrous state (Fe²⁻; FeO) is ablue-green colorant, while iron in the ferric state (Fe³⁺) is ayellow-green colorant. The blue-green colorant of ferrous iron (Fe²⁺;FeO) is of particular concern when seeking to achieve a fairly clear orneutral colored glass, since as a strong colorant it introducessignificant color into the glass. While iron in the ferric state (Fe³⁺)is also a colorant, it is of less concern when seeking to achieve aglass fairly clear in color since iron in the ferric state tends to beweaker as a colorant than its ferrous state counterpart.

In certain example embodiments of this invention, a glass is made so asto be highly transmissive to visible light, to be fairly clear orneutral in color, and to consistently realize high % TS values. High %TS values are particularly desirable for photovoltaic deviceapplications in that high % TS values of the light-incident-side glasssubstrate permit such photovoltaic devices to generate more electricalenergy from incident radiation since more radiation is permitted toreach the semiconductor absorbing film of the device. It has been foundthat the use of an extremely high batch redox in the glass manufacturingprocess permits resulting low-ferrous glasses made via the float processto consistently realize a desirable combination of high visibletransmission, substantially neutral color, and high total solar (% TS)values. Moreover, in certain example embodiments of this invention, thistechnique permits these desirable features to be achieved with the useof little or no cerium oxide.

In certain example embodiments of this invention, a soda-lime-silicabased glass is made using the float process with an extremely high batchredox. An example batch redox which may be used in making glassesaccording to certain example embodiments of this invention is from about+26 to −40, more preferably from about +27 to +35, and most preferablyfrom about +28 to +33 (note that these are extremely high batch redoxvalues not typically used in making glass). In making the glass via thefloat process or the like, the high batch redox value tends to reduce oreliminate the presence of ferrous iron (Fe²⁺; FeO) in the resultingglass, thereby permitting the glass to have a higher % TS transmissionvalue which may be beneficial in photovoltaic applications. This isadvantageous, for example, in that it permits high transmission, neutralcolor, high % TS glass to be made using raw materials having typicalamounts of iron in certain example instances (e.g., from about 0.04 to0.10% total iron). In certain example embodiments of this invention, theglass has a total iron content (Fe₂O₃) of no more than about 0.1%, morepreferably from about 0 (or 0.04) to 0.1%, even more preferably fromabout 0.01 (or 0.04) to 0.08%, and most preferably from about 0.03 (or0.04) to 0.07%. In certain example embodiments of this invention, theresulting glass may have a % FeO (ferrous iron) of from 0 to 0.0050%,more preferably from 0 to 0.0040, even more preferably from 0 to 0.0030,still more preferably from 0 to 0.0020, and most preferably from 0 to0.0010, and possibly from 0.0005 to 0.0010 in certain example instances.In certain example embodiments, the resulting glass has a glass redox(different than hatch redox) of no greater than 0.08, more preferably nogreater than 0.06, still more preferably no greater than 0.04, and evenmore preferably no greater than 0.03 or 0.02.

In certain example embodiments, the glass substrate may have fairlyclear color that may be slightly yellowish (a positive b* value isindicative of yellowish color), in addition to high visible transmissionand high % TS. For example, in certain example embodiments, the glasssubstrate may be characterized by a visible transmission of at leastabout 90% (more preferably at least about 91%), a total solar (% TS)value of at least about 90% (more preferably at least about 91%), atransmissive a* color value of from −1.0 to +1.0 (more preferably from−0.5 to +0.5, even more preferably from −0.35 to 0), and a transmissiveb* color value of from −0.5 to +1.5 (more preferably from 0 to +1.0, andmost preferably from +0.2 to +0.8). These properties may be realized atan example non-limiting reference glass thickness of about 4 mm.

In certain example embodiments of this invention, there is provided amethod of making glass comprising:

Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO  5-15% total iron(expressed as Fe₂O₃) 0.001 to 0.1% % FeO     0 to 0.005wherein the glass has visible transmission of at least about 90%, atransmissive a* color value of −1.0 to +1.0, a transmissive b* colorvalue of from −0.50 to −1.5, % TS of at least 89.5%, and wherein themethod comprises using a batch redox of from +26 to +40 in making theglass.

In certain example embodiments of this invention, there is provided aglass comprising:

Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO  5-15% total iron(expressed as Fe₂O₃) <= 0.1% % FeO <= 0.005 glass redox <= 0.08 antimonyoxide 0 to less than 0.01% cerium oxide 0 to 0.07%wherein the glass has visible transmission of at least 90%, TStransmission of at least 90%; a transmissive a* color value of −1.0 to+1.0, a transmissive b* color value of from −0.5 to +1.5.

In still further example embodiments of this invention, there isprovided solar cell comprising: a glass substrate; first and secondconductive layers with at least a photoelectric film providedtherebetween; wherein the glass substrate is of a compositioncomprising:

Ingredient wt. % SiO₂ 67-75% Na₂O 10-20% CaO  5-15% total iron(expressed as Fe₂O₃) <= 0.1% % FeO <= 0.005 glass redox <= 0.08 antimonyoxide 0 to less than 0.01% cerium oxide 0 to 0.07%wherein the glass substrate has visible transmission of at least 90%, TStransmission of at least 90%; a transmissive a* color value of −1.0 to+1.0, a transmissive b* color value of from −0.5 to +1.5.

As used herein, the terms “on,” “supported by,” and the like should notbe interpreted to mean that two elements are directly adjacent to oneanother unless explicitly stated. In other words, a first layer may besaid to be “on” or “supported by” a second layer, even if there are oneor more layers therebetween.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of making a lens array for use in asolar photovoltaic module, the method comprising: making glass using afloat process including a float glass line; and patterning the glassusing a plurality of rollers disposed along the float glass line so asto form a plurality of first lenses oriented along a common axis,wherein the rollers each have profiles such that each said first lens ispatterned to have at least one convex major surface when viewed in sidecross section, wherein the plurality of rollers comprise top and bottomrollers, and wherein the patterning is performed such that each saidfirst lens has two convex major surfaces when viewed in side crosssection on respective opposing major surfaces thereof so that each lenshas convex surfaces on opposite sides thereof, and wherein each saidlens has a focal length of about 10-200 nm.
 2. The method of claim 1,wherein the lens array is a Fresnel lens array.
 3. The method of claim1, further comprising thermally tempering the lenses in the lens array.4. The method of claim 1, further comprising wet-applying anantireflective coating to one or both major surfaces of the lens array.5. The method of claim 1, wherein each said lens has a width of about10-100 mm, a minimum thickness of about 2-4 mm, and a maximum thicknessof about 4-8 mm.
 6. The method of claim 4, wherein each said lens has awidth of about 10-100 mm, a minimum thickness of about 2-4 mm, and amaximum thickness of about 4-8 mm.